The present invention relates generally to systems and methods for monitoring the flight parameters of an aircraft and, more particularly, to apparatus, methods, and computer program products for monitoring the attitude of an aircraft in order, for example, to provide an alternative indication to the pilot of an aircraft""s attitude in a cost effective manner.
An important, concern in the aircraft industry is ensuring flight safety. In light of this, many advancements have been made in the past few years to provide pilots and flight crew of aircraft with increased awareness concerning aircraft performance, flight parameters, and proximity of terrain and obstacles to the aircraft. For example, many of today""s commercial and military grade aircraft include extensive instrumentation for providing the pilot and flight crew with a wide range of information concerning performance and flight parameters of the aircraft. Additionally, ground proximity warning systems, (also known as terrain awareness systems), have been developed, which analyze the flight parameters of the aircraft and the terrain surrounding the aircraft. Based on this analysis, these warning systems provide alerts to the flight crew concerning possible inadvertent collisions of the aircraft with surrounding terrain or other obstacles.
Providing flight safety systems for general aviation aircraft, however, has been somewhat problematic. Although flight safety is important, the cost and size of flight safety instrumentation and systems make these systems less feasible for smaller, less costly general aviation aircraft. As such, many of today""s general aviation aircraft include less sophisticated instruments, and provide less information to the pilot and flight crew concerning aircraft operation and flight parameters than commercial and military grade aircraft. To remedy some of these problems, a ground proximity warning system has been developed by the Assignee of the present application for use in general aviation aircraft. This ground proximity warning system uses less inputs than ground proximity warning systems used in commercial and military grade aircraft to thereby accommodate for the reduced number of instruments available in the general aviation aircraft. This ground proximity warning system is described in U.S. patent application Ser. No. 09/534,222, entitled xe2x80x9cGround Proximity Warning System And Method Having A Reduced Set Of Input Parametersxe2x80x9d filed on Mar. 24, 2000.
Despite the introduction of a ground proximity warning system for use in general aviation aircraft, there still remains a need for additional safety systems to provide the pilot and flight crew of general aviation aircraft with increased awareness concerning the flight operation and parameters of the aircraft. For example, many general aviation aircraft typically include an attitude indicator device, (also known as an artificial horizon). The attitude indicator provides both pitch and bank angle of the aircraft relative to Earth. For example, FIG. 1 illustrates a typical attitude indicator. The attitude indicator of FIG. 1 indicates that the aircraft associated with the attitude indicator is in a climbing turn.
Knowledge of the aircraft attitude with reference to Earth is very important for flight safety. Specifically, when the aircraft is flown either in inclement weather conditions, such as rain or fog, or at night, the pilot and flight crew cannot reference the plane""s orientation with the earth""s surface based on the ground below or the natural horizon. In these instances, the pilot and flight crew generally rely on the attitude indications provided by the attitude indicator for safe navigation. As such, it is important that the attitude indicator provide an accurate indication of the attitude of the aircraft, so that the aircraft may be safely flown in inclement weather conditions or at night.
However, there may be some accuracy problems associated with attitude indicators used in many aircraft. Specifically, attitude indicators are typically gyroscopic devices that operate on a vacuum source, which powers and spins the gyroscope. As illustrated in FIG. 1, as the aircraft changes pitch and bank angle, the gyroscope remains positioned level with the earth""s surface, thereby indicating the aircraft""s orientation relative to earth. Problems may occur when the vacuum pump either malfunctions or fails. In this instance, the attitude indicator will not accurately reflect the attitude of the aircraft. Even more problematic is the fact that this is typically not an abrupt event, but instead, the vacuum system typically fails in a gradual manner. As such, there may be a time frame in which the attitude indicator is providing erroneous indications, but not noticeably incorrect readings. Thus, if the pilot does not cross-check the attitude indicator against other cockpit instruments, he or she may make control inputs based on this erroneous information and position the aircraft in an unsafe attitude.
The problems associated with attitude indicator failure are generally not a major concern for commercial and military grade aircraft, as these aircraft include alternative sources of attitude information. For example, many of these aircraft include systems such as inertial navigation systems (INS). The INS includes three accelerometers mounted perpendicular to each other and three rate gyroscopes that measure the rate of movement of the aircraft about the pitch, roll, and yaw axes. The INS is often used in the aircraft auto-pilot systems to maintain the aircraft in a safe attitude. The INS can also be used by the pilot and flight crew as an alternative or back-up system to the attitude indicator.
Additionally, attitude systems have been developed using global positioning systems (GPS). These attitude systems include three GPS antennas that are located at different positions on the body of the aircraft. Each of the GPS antennas provides a position of the aircraft corresponding to the position of the body of the aircraft to which the GPS antenna is attached. By comparing the positions output by each of the GPS antennas, the pitch, roll, and yaw of the aircraft can be determined.
Although these INS and GPS based attitude systems provide alternative or back-up systems for monitoring the attitude of an aircraft, these systems may not be feasible for use in some aircraft. Specifically, these systems are typically expensive, are of significant size and weight, and require ancillary equipment to support these systems. As such, a system for monitoring and providing an alternative indication of the attitude of the aircraft to the pilot and flight crew that is more cost effective, reduced in size and weight, and requires less ancillary equipment is needed for use in general aviation aircraft, as well as other types of aircraft.
As set forth below, the present invention provides apparatus, methods, and computer program products for monitoring the attitude of an aircraft. Importantly, the apparatus, methods, and computer program products of the present invention use the velocity vector generated by a single GPS antenna and the sensed roll and pitch angles of the aircraft generated by a pair of low cost gyroscopes to provide an indication of the attitude of the aircraft. By using a single GPS antenna and a pair of low cost gyroscopes, the apparatus, methods, and computer program products of the present invention provide a low cost alternative aircraft attitude indicator that can be used either in place of or in conjunction with the traditional attitude indicator of the aircraft.
Accordingly, in one embodiment, the present invention includes an apparatus for monitoring the attitude of an aircraft. The apparatus includes both an input for receiving velocity values related to the velocity vector of the aircraft and an output for providing a composite roll and flight path angle of the aircraft. Connected to the input is a generator for determining a calculated flight path angle and a calculated roll angle of the aircraft based on a velocity vector of the aircraft. Further, the apparatus of the present invention includes a first combiner in electrical communication with the generator for combining the calculated flight path angle from the generator with a sensed pitch angle of the aircraft and the calculated roll angle from the generator with a sensed roll angle of the aircraft.
In operation, the apparatus initially receives, via the input, velocity values representing the velocity vector of the aircraft. Based on these velocity vectors, the generator generates calculated flight path and roll angles. The first combiner receives the calculated flight path and roll angles and combines these values with corresponding sensed pitch and roll angles of the aircraft to thereby produce a composite flight path angle and a composite roll angle representing the attitude of the aircraft. These composite flight path and roll angels are provided to the output of the apparatus.
As detailed above, the first combiner of the present invention combines the calculated flight path and roll angles with sensed pitch and roll angles of the aircraft. In one embodiment, the apparatus of the present invention further includes first and second gyroscopes positioned with respect to the aircraft such that one of the gyroscopes senses the roll angle of the aircraft and the other senses the pitch angle of the aircraft. In operation, as the aircraft moves relative to the pitch and roll axes, the gyroscopes sense these movements and output sensed roll and pitch angles to the first combiner.
In some embodiments of the present invention, the first and second gyroscopes are rate gyroscopes having outputs that represent the rate of change in the roll and pitch of the aircraft. In this embodiment, to determine a sensed pitch and roll angle, the apparatus further includes first and second integrators connected respectively to the first and second gyroscopes. The first and second integrators integrate the respective outputs of the first and second gyroscopes to provide sensed roll and pitch angles of the aircraft to the first combiner.
As discussed above, the apparatus of the present invention includes both a GPS antenna and gyroscopes for determining the attitude of the aircraft. Use of both the GPS antenna and the gyroscopes is important in providing an accurate indication of the attitude of the aircraft. Specifically, GPS is typically an accurate and reliable system for providing positional information related to the aircraft. However, due to the need to calculate the flight path angle and the pitch from the velocity vector values generated by the GPS and the typically slower refresh rate of GPS, the attitude information provided by GPS may lag somewhat behind the actual movement of the aircraft.
Additionally, as stated, the generator generates a calculated roll angle based on the velocity vector of the aircraft and more particularly, based on the change in track of the aircraft over time. Specifically, if the aircraft has a roll angle other than 0xc2x0, then typically the track of the aircraft with respect to north will change over time. Thus, typically by monitoring the change in track over time, the roll of the aircraft is determinable. However, in some flight maneuvers, the aircraft may have a roll angle other than 0xc2x0, but the track of the aircraft does not change. For example, if an aircraft is landing in a cross-wind, many times the pilot will perform a xe2x80x9cslide slipxe2x80x9d maneuver, in which the aircraft is banked to counteract the cross-wind so that the aircraft will fly at a constant track. In this instance, the generator will generate a 0 value for the calculated roll angle because there is no change in track, even though the aircraft has a roll angle different from 0xc2x0.
In light of this, the gyroscopes are used to track and provide more frequent updates of the aircraft""s movements to thereby supplement the output of the GPS. Further, in instances, in which the aircraft has a roll angle but is not changing track, the gyroscopes will sense the roll of the aircraft and provide the roll angle value. However, these gyroscopes are typically less accurate over time and may begin to drift. As such, in some embodiments, the output of the GPS is used to monitor the attitude of the aircraft for stable flight, while the gyroscopes are used for abrupt changes in the attitude of the aircraft.
In order to combine the signals from the GPS and the gyroscopes such that the calculated angle values of the GPS are used for stable flight and the angle values from the gyroscopes are used for abrupt changes, the first combiner, according to one embodiment of the present invention, further includes a complimentary filter connected to the output of the generator and the first and second gyroscopes. The complimentary filter operates as a low pass filter for the output of the generator and a high pass filter for the output of the first and second gyroscopes. As such, for stable flight, the calculated angle values from the generator and GPS dominate the composite flight path and roll angle values used for indicating the attitude of the aircraft, while during abrupt changes in the aircraft""s orientation, the output of the gyroscopes dominate the composite flight path and roll angle values used for indicating the attitude of the aircraft.
As mentioned above, the generator generates a calculated flight path and roll angle based on the velocity vector of the aircraft. In one embodiment of the present invention, the apparatus further includes a navigation system connected to the input. The navigation system provides an indication of the velocity of the aircraft in a north (Vn), east (Ve), and vertical (Vz) direction. In this embodiment of the present invention, the generator determines a calculated flight path angle and a calculated roll angle of the aircraft based on the velocity of the aircraft in a north (Vn), east (Ve), and vertical (Vz) direction. For example, in one embodiment, the generator determines the calculated flight path angle and calculated roll angle of the aircraft based on the following equations:       γ    =                  tan                  -          1                    ⁢                        V          z                                                    V              n              2                        +                          V              e              2                                                ψ    =                  tan                  -          1                    ⁢                        V          n                          V          e                                Roll      w        =                  tan                  -          1                    ⁢                                                  ⅆ              ψ                                      ⅆ              t                                ⁢                                                    V                n                2                            +                              V                e                2                                                    g            
where
xcex3=calculated flight path angle of the aircraft;
"psgr"=track angle of the aircraft;
Rollvv=calculated roll angle of the aircraft;
Vn=velocity of the aircraft in a north direction;
Ve=velocity of the aircraft in an east direction;
Vz=velocity of the aircraft in a vertical direction; and
g=gravity.
In addition to generating composite flight path and roll angles indicating the attitude of the aircraft, in some embodiments, the apparatus, methods, and computer program products of the present invention may also monitor the attitude of the aircraft and provide the pilot with alerts, either visual or aural, if the aircraft is oriented at an unsafe attitude. For example, in one embodiment of the present invention, the apparatus further includes a comparator connected to the output of the first combiner and an alert device connected to the comparator. In operation, the comparator compares the composite roll angle generated by the first combiner to a threshold roll angle. If the composite roll angle is at least as great as the threshold roll angle, the alert device will provide an alert to the pilot that the aircraft is in an unsafe roll or bank angle orientation. In some embodiments, the apparatus further includes a display connected to the output comparator that displays the composite flight path angle and composite roll angle indicating the attitude of the aircraft.
In addition to providing alerts concerning an excessive bank angle, the apparatus, methods, and computer program products of the present invention also monitor the flight path angle of the aircraft. For example, in one embodiment of the present invention, the comparator connected to the output of the first combiner compares the composite flight path angle generated by the first combiner to upper and lower threshold flight path angles. If the composite flight path angle is at least great as the upper threshold flight path angle or no more than the lower flight path angle, the alert device will generate an indication to the pilot of the aircraft. Further, in some embodiments, the display may display the composite flight path angle and composite roll angle indicating the attitude of the aircraft.
As discussed previously, the traditional attitude indicator used in most aircraft may experience either an abrupt or gradual failure that may cause the pilot to place the aircraft in an unsafe attitude. In light of this, in some applications, it is advantageous to use the apparatus, methods, and computer program products of the present invention as a redundant system so that failures in the traditional attitude indicator can be recognized by the pilot. For example, in one embodiment of the present invention, the apparatus further includes a second combiner connected to the output of the first combiner. The second combiner is also connected to an output of a traditional attitude indicator associated with the aircraft. The apparatus of this embodiment also includes a comparator connected to the output of the second combiner.
In operation, the second combiner combines the composite roll angle from the first combiner with an indicated roll angle provided by the attitude indicator associated with the aircraft and generates a difference signal. The comparator of this embodiment, in turn, compares the difference signal to a difference angle threshold value. If the difference signal is at least as great as the difference angle threshold value, the alert device generates an indication to the pilot notifying the pilot that the attitude indicator associated with the aircraft may be incorrect. As such, the pilot will not use the traditional attitude indicator, but instead, will rely on the composite flight path and roll angle output by the apparatus, methods, and computer program products of the present invention.
Importantly, as mentioned above, the apparatus, methods, and computer program products of the present invention use values from a single GPS antenna and two low cost rate gyroscopes to provide an indication of the attitude of the aircraft. As a single GPS antenna and low cost gyroscopes are much more cost effective, smaller in size and weight, and require less ancillary equipment than either multiple GPS antennas of INS systems, the apparatus, methods, and computer program products of the present invention provide a feasible attitude monitoring system for use in aircraft, and especially in general aviation aircraft where cost, size, and weight are significant factors.